Dont know if anyone saw the pics of a car transporter with 6 Subaru cars on but they took the top 3 off and heres the result (camera fone so not very good pics)
they use a mirror hun, and then the end of the truck pivots round so all cars are upright and unload as normal then.
nahh i'm joking, here is text from their site:
The 'Subaglue' campaign was devised by London-based advertising agency, MCBD and the three upside-down cars were bolted to the upper deck after having their engines and transmissions removed.